One of the standard methods for imaging a surface, particularly the surface of a semiconductor wafer, is to irradiate the surface with an electron beam in an electron microscope. Secondary electrons from the surface are collected, and may be used to form an image of the irradiated surface. Typically, in order to image the complete surface of the wafer, the electron beam is scanned across the surface, and the surface is moved orthogonally to the direction of the scanned beam.
Electron beam images may exhibit a low signal to noise (SNR) ratio and may suffer from unwanted charging effects.
There is a growing need to reduce charging effects and to increase the signal to noise ratio of electron beam images.